In recent years, attention has been given to hybrid vehicles and electric vehicles that run using an drive power provided by an electric motor, against the background of environmental issues. These vehicles are equipped with a power storage mechanism formed of a secondary battery, an electric double-layer capacitor or the like for supplying a power to a drive source, i.e., the electric motor, for converting an kinetic energy into an electric energy during regenerative braking and for storage. Discharging from the power storage mechanism and the charging of the power storage mechanism are performed in view of an SOC (State of Charge) of the power storage mechanism. By keeping the SOC within an appropriate range, the overcharging and overdischarging of the power storage mechanism can be avoided.
In the vehicle that uses the above electric motor as a drive power source, it is desired to increase the charge/discharge capacity of the power storage mechanism for increasing running performance such as acceleration performance and a continuous travel distance without. A structure equipped with a plurality of power storage mechanisms has been proposed as a configuration for increasing the charge/discharge performance of the power storage mechanism.
For example, Japanese Patent Laying-Open No. 2003-209969 (Patent Document 1) has disclosed a power supply control system that has at least one inverter for supplying a regulated power to an electric tractive motor of a vehicle as well as a plurality of power supply stages each having a battery and a boost/back DC-DC converter. These power storage stages are electrically connected in parallel for supplying a DC power to the at least one inverter, and are controlled to keep an output voltage to the at least one inverter.    Patent Document 1: Japanese Patent Laying-Open No. 2003-209969    Patent Document 2: Japanese Patent Laying-Open No. 7-191109    Patent Document 3: Japanese Patent Laying-Open No. 11-055866    Patent Document 4: Japanese Patent Laying-Open No. 11-164488    Patent Document 5: Japanese Patent Laying-Open No. 10-341540    Patent Document 6: Japanese Patent Laying-Open No. 9-182311    Patent Document 7: Japanese Patent Laying-Open No. 2001-037097